Deliberate incompetence makes for better lithium-air batteries

Researchers keep the airways of a lithium air battery open and demonstrate the …

Lithium-air batteries are the coming thing. They have the potential to hold ten times the capacity per unit volume of lithium-ion batteries and are lighter, since one of the charge-carrying materials is ambient air. These air-breathing monsters look great. But, as with all monsters, they have their vulnerable spot. In this case, the vulnerability is something akin to asthma—the inability to get enough air into the battery. Medical scientists don`t seem to be too interested in making inhaler products for batteries, though, so scientists have been trying to come up with ways to keep the air flowing.

In some recent work, published in Nano Letters, researchers show that producing graphene as poorly as possible helps a lot. Yes, it truly is a case of deliberate incompetence saving the day.

Aside from the drama of monsters with asthma, why are we interested in lithium-air batteries anyway? The key is energy storage. You can only pack so many lithium ions into a given space. Given that limit, the amount of energy you get out depends on the reaction potential at the electrodes, which are typically graphite—graphene's poor country cousin. Clearly, a serious change in technology is required if we are to meet the demands of the future: electric cars don't run on air, you know.

In a lithium air battery, one of the electrodes is the lithium itself and its reaction with air takes place at a conducting carbon electrode. But the end product of the reaction is lithium oxide, which isn't soluble. So, lithium turns up at the electrode, reacts with the oxygen in the air, and the departing electrons leave behind a little lithium oxide deposit. Eventually, these deposits clog up the system and the battery dies a slow, gasping death.

To overcome this problem, a team from Pacific Northwest National Laboratory and Princeton have taken an idea from nature. Smokers face the same problem the battery does every day. Every cigarette that they smoke leaves behind some particulate matter that reduces lung function. Yet, smokers generally go for many years before their reduced lung capacity becomes noticeable.

This is because the lung consists of a branching network, where the tiny alveoli—the point where oxygen enters the blood stream—are never very far away from a big tube, one that's too big to be easily blocked. There are lots and lots of alveoli, so you can afford to lose a few, but the big tubes make sure that losing an alveoli due to blockage doesn't block up neighboring alveoli.

The question then is, how do you do this in carbon? It turns out to be not too difficult. Take one lump of graphite oxide and begin to remove the oxygen. As the oxygen is removed at high temperature, the graphite expands into many graphene sheets, tearing itself to pieces to create micrometer sized holes throughout the structure. Each graphene sheet still has a fair bit of oxygen associated with it, which are defects that create nanometer-sized holes in the graphene sheets. The result is the lowest-quality graphene known to man—something to be proud of in itself—and a lovely network of tiny reaction centers, interconnected by big tubes.

The cool thing is that the balance between the large holes that provide the main air tubes and the small holes that play the role of reaction sites can be controlled just by playing with the amount of time spent removing the oxygen from the graphite oxide. The researchers tried a number of different ratios and found that leaving just one percent of the oxygen behind gave the best battery performance.

If that wasn't enough to make you fall in love with the monster, there is another advantage to this electrode. The lithium oxide deposits should still eventually clog things up, but something unexpected—unexpected to me, anyway—happens. The lithium oxide deposits are only stable up to clumps of five units. That is, when a sixth lithium oxide molecule tries to join the party, the clump is likely to fall apart, keeping the lumps small and maintaining open airways.

Finally, the information you have all been waiting for: how much energy can I get from this battery? The researchers demonstrated 15000mAhr per gram of carbon electrode. And that seems pretty fantastic to me.

So, as my kids say to me: are we there yet? Nearly. The capacity measurements that they showed were taken at twice atmospheric pressure, so there is some question about how the batteries would perform at atmospheric pressure and 20 percent oxygen. Then there is the question of recharging. In principle, lithium air batteries are rechargeable, but a metallic catalyst at the carbon electrode is required. In this work, the researchers did not include the catalyst, so no recharging.

Even so, this is the right path to take: this beast no longer gasps for air. With more optimization, metal catalysts can be worked into the mix.

Chris Lee
Chris writes for Ars Technica's science section. A physicist by day and science writer by night, he specializes in quantum physics and optics. He lives and works in Eindhoven, the Netherlands. Emailchris.lee@arstechnica.com//Twitter@exMamaku

Are these the types of cells that you could see in personal electronics or are they not really applicable? I only ask because it's the one aspect of my life where increased battery life would make an obvious impact.

Also what about other things that use storage cells? Cars? Electrical grid? What kind of applications do people expect to see for these new cells?

Please, please, leave the "cool speak" to the kids and write more simply and clearly. There is no need for,"These air-breathing monsters look great. But, as with all monsters, they have their vulnerable spot.", or for, "Medical scientists don`t seem to be too interested in making inhaler products for batteries...". Those are just in the first paragraph.

Now that the Grammar Nazis have had their say on the article, I have to say - awesome article!

I for one didn't care if you got the singular and plural mixed up on some words or had an extra word that wasn't necessary.

I DID however care that you posted a timely article about a very interesting subject - and presented it in a stylishly humorous and educational manner that helped me to understand the future of our high tech batteries.

Please, please, leave the "cool speak" to the kids and write more simply and clearly. There is no need for,"These air-breathing monsters look great. But, as with all monsters, they have their vulnerable spot.", or for, "Medical scientists don`t seem to be too interested in making inhaler products for batteries...". Those are just in the first paragraph.

I thought it was pretty amusing, and as a teenager I'm legally allowed to define "cool speak".

Please, please, leave the "cool speak" to the kids and write more simply and clearly. There is no need for,"These air-breathing monsters look great. But, as with all monsters, they have their vulnerable spot.", or for, "Medical scientists don`t seem to be too interested in making inhaler products for batteries...". Those are just in the first paragraph.

I thought it was pretty amusing, and as a teenager I'm legally allowed to define "cool speak".

I thought it definitely added to the article, and, as a 33 year old who still talks about his plans for when he grows up, I'm legally allowed to be a hipster.

I would assume that popping something like this (but rechargeable obviously) on the front of an electric car behind the conventional cooling vent grille might provide sufficient air flow to keep it going well. If so would the additional density offset the manufacturer's restrictions on battery placement (normally low and centrally located to reduce moment of inertia and crash survivability amongst other things I assume?)

When you say "5000mAhr per gram of carbon electrode", what does that mean in terms of a cellphone size battery?

The units of mAhr (current*time, specific capacity) are kind of meaningless unless you know the operating voltage. You can calculate the energy density by multiplying this by the average voltage that the battery can produce (2.65 V), which gives you 39714 Wh/kg of carbon.

The paper kept using the metric of .../g of carbon. Now, lithium air batteries are lighter in part because of this lightweight carbon cathode, but the battery capacity is determined by the lithium anode. Therefore, this paper really is only talking about their new ability to reduce the weight of the carbon cathode while maintaining proper battery function.

In theory, this technology could give you either a smaller battery for a given capacity or a larger capacity for a given size. Like all news stories dealing with battery breakthroughs, though, you shouldn't hold your breath. They still need to get this to work at atmospheric pressure, and then they need to make sure that it is rechargeable. Finally, their technology would need to be easy to make on a large scale without having a dramatic increase in price. There are a lot of hurdles left to go, but this is an interesting piece of the puzzle.

This stuff is going to redefine our civilisation. These guys deserve all the support we can offer to get this in mass production. All these new technologies are great on a lab bench but they need to be out there. If they can achieve 10 fold increase in energy density we are talking cars that can do 2000 miles on a charge. or crazy speeds, we are talking realistic grid storage for solar wind and hydro energy. This is a small part of a large jigsaw which is being put together to ensure we can move along from the trick we learned 10000 years ago, setting fire to stuff. If you think about it, we have got better at harvisting the energy from that reaction but we haven't really changed anything fundementallly in a very long time. Setting fire to stuff is still the best way we have to run our lives. isn't it time we found a new neet trick? This is part of the puzzle which allows us to move to the next big thing. Hopefully in 50 years, energy will be something we can take for granted. instead of fighting over it, killing one another for it etc.

Please, please, leave the "cool speak" to the kids and write more simply and clearly. There is no need for,"These air-breathing monsters look great. But, as with all monsters, they have their vulnerable spot.", or for, "Medical scientists don`t seem to be too interested in making inhaler products for batteries...". Those are just in the first paragraph.

Now that the Grammar Nazis have had their say on the article, I have to say - awesome article!

I for one didn't care if you got the singular and plural mixed up on some words or had an extra word that wasn't necessary.

I DID however care that you posted a timely article about a very interesting subject - and presented it in a stylishly humorous and educational manner that helped me to understand the future of our high tech batteries.

@BinaryFu, it is entirely okay to be timely, humorous, educational, and grammatically accurate at the same time.

Please, please, leave the "cool speak" to the kids and write more simply and clearly. There is no need for,"These air-breathing monsters look great. But, as with all monsters, they have their vulnerable spot.", or for, "Medical scientists don`t seem to be too interested in making inhaler products for batteries...". Those are just in the first paragraph.

Lighten up, this isn't a Scientific Journal and most of us like the levity.

Please, please, leave the "cool speak" to the kids and write more simply and clearly. There is no need for,"These air-breathing monsters look great. But, as with all monsters, they have their vulnerable spot.", or for, "Medical scientists don`t seem to be too interested in making inhaler products for batteries...". Those are just in the first paragraph.

I thought it was pretty amusing, and as a teenager I'm legally allowed to define "cool speak".

I thought it definitely added to the article, and, as a 33 year old who still talks about his plans for when he grows up, I'm legally allowed to be a hipster.

...

Wait, I think that came out wrong.

I'll go ahead and push the age up by another decade. I still feel like a kid and am often surprised by the curmudgeon staring back at me from the mirror. I thought it added a light and humorous touch to an excellent science article.

Please, please, leave the "cool speak" to the kids and write more simply and clearly. There is no need for,"These air-breathing monsters look great. But, as with all monsters, they have their vulnerable spot.", or for, "Medical scientists don`t seem to be too interested in making inhaler products for batteries...". Those are just in the first paragraph.

Yeah, I'm 44 yo, relatively uncool and I liked that part. It was clever, funny and clear. What's the problem?

Anyways...

I'm always interested in new battery tech as what we have today is rather inadequate. My interests, besides computers, are in outdoor and bicycle products. Is this technology targeted solely at larger laptop/tablet batteries or they'll come in smaller sizes such as AA? So I wonder if these type of battery will be able to drive something like CREE headlights that draw constant high current. Also, what about charging time and shelf life? At ten times the capacity of today's batteries how long would it take to charge? Will they require wall outlet to charge or will they also charge from weaker sources such as USB or portable solar panels?

I have to say, these science articles by Chris have become my favorite on Ars. I started coming here way back in the day for the computer geekery (and I still do) but I find myself enjoying the science articles, and the commentary they spawn, the most; especially since the comments seem to be much higher quality and often as enlightening as the article. Keep it up!

People keep asking what this means in terms of a battery. I'm too into LoL right now but Lithium Air batteries theoretical specific energy is 40.1 MJ/kg , Your Lithium Ion in cell phones and laptops is 0.46 MJ/kg, and Gasoline is 44 MJ/kg. Just take the rough idea and say Hell YEA!

I enjoyed the content but put my vote with "please scale down the cute stuff ever so slightly."

Twice atmospheric pressure sounds like an interesting challenge to overcome. Not as if a battery that breathes is going to efficiently pump up its internal pressure. On the other hand, if the improvement is "only" 5x over conventional batteries then I am still excited!

Please, please, leave the "cool speak" to the kids and write more simply and clearly. There is no need for,"These air-breathing monsters look great. But, as with all monsters, they have their vulnerable spot.", or for, "Medical scientists don`t seem to be too interested in making inhaler products for batteries...". Those are just in the first paragraph.

I'm already surprised how far we have come...I currently use LiPo batteries for my Underground headlamp, and compared to the old Lead Acid cells on a traditional miners lamp, (with an almost identical capacity), they are a fraction of the weight. Now, if they could pack a lot more energy into that space, I would suspend my normal restraint and become a very early adopter. Hopefully the lampbuilders will catch up... a lot of them think that Li-Ion is the bees knees with regards to energy density.

Energy capacity per unit of weight is nearly meaningless for small gadgets. Of course weight matters, but more importantly: wha'ts the capacity per unit of volume, and how does it compare to current Li-Ion batteries?

While I'm at it - would the metal catalyst used for recharging have any effect on storage capacity? Would these batteries suffer from memory effect? How many cycles could one of these batteries go through without substantial performance reduction?

Chris, "15000mAhr per gram of carbon electrode" is pretty meaningless to most people.Can you indicate how much energy the whole battery (not just the electrode) can provide, and can you also provide it in a comparative unit we can relate to, like how many times more energy this battery stores for the same volume, not weight, as a specific iPhone or laptop or electrical car model?The amount of energy per weight only is useful only for static batteries, but mobile applications require both weight and volume performance.

Very interesting development, thanks to Ars for drawing attention to this sort of development. But also put my vote with "A little less cute, a little more explanation of the facts". The 150000 figure was not particularly helpful without context.

People keep asking what this means in terms of a battery. I'm too into LoL right now but Lithium Air batteries theoretical specific energy is 40.1 MJ/kg , Your Lithium Ion in cell phones and laptops is 0.46 MJ/kg, and Gasoline is 44 MJ/kg. Just take the rough idea and say Hell YEA!

I knew that the lithium/air batteries energy density was high but I can never remember the density for things like gasoline. Thanks for the awe inspiring comparison and here is your requested Hell YEA!!